PDP-11 Chess VI (Belle) By Ken Thompson (1973) ported

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Jim Ablett
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Location: London, England
Full name: Jim Ablett

Re: PDP-11 Chess VI (Belle) By Ken Thompson (1973) ported

Post by Jim Ablett »

jasper.sinclair wrote: Sun May 17, 2026 6:31 pm Nice work Jim Ablett! I have spent some time on this historic engine (Jim's port), it and have managed to add
full UCI support
and the ability to parse positions w/ FEN (both in Winboard and UCI)
You can also call create_book directly from the UCI command line.

https://github.com/jasper-sinclair/PDP- ... s-VI-Belle

I'll add a perft function soon so we can see how move generation performs.
Wow! great work Jasper.

best,
Jim.
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jasper.sinclair
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Re: PDP-11 Chess VI (Belle) By Ken Thompson (1973) ported

Post by jasper.sinclair »

perft divide added

chess6.exe -uci -nobook -post
perft 6
a2a3: 4463267
a2a4: 5363555
b2b3: 5310358
b2b4: 5293555
c2c3: 5417640
c2c4: 5866666
d2d3: 8073082
d2d4: 8879566
e2e3: 9726018
e2e4: 9771632
f2f3: 4404141
f2f4: 4890429
g2g3: 5346260
g2g4: 5239875
h2h3: 4463070
h2h4: 5385554
b1c3: 5708064
b1a3: 4856835
g1h3: 4877234
g1f3: 5723523
nodes 119060324
time 2875 ms
nps 41412286

I'm really not sure how strong this engine is...
Apparently; it was the first machine to achieve master-level play (2250 USCF rating in 1983).
This version however appears to be from 1973...I haven't tested it, but when I see it play it appears to be club level, 1800, 2000? :?:
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Jim Ablett
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Re: PDP-11 Chess VI (Belle) By Ken Thompson (1973) ported

Post by Jim Ablett »

jasper.sinclair wrote: Sun May 17, 2026 9:50 pm perft divide added

chess6.exe -uci -nobook -post
perft 6
a2a3: 4463267
a2a4: 5363555
b2b3: 5310358
b2b4: 5293555
c2c3: 5417640
c2c4: 5866666
d2d3: 8073082
d2d4: 8879566
e2e3: 9726018
e2e4: 9771632
f2f3: 4404141
f2f4: 4890429
g2g3: 5346260
g2g4: 5239875
h2h3: 4463070
h2h4: 5385554
b1c3: 5708064
b1a3: 4856835
g1h3: 4877234
g1f3: 5723523
nodes 119060324
time 2875 ms
nps 41412286

I'm really not sure how strong this engine is...
Apparently; it was the first machine to achieve master-level play (2250 USCF rating in 1983).
This version however appears to be from 1973...I haven't tested it, but when I see it play it appears to be club level, 1800, 2000? :?:
I think that 2250 rating is for the dedicated hardware version not the earlier software version which my port is. I think engine is around 1500/1600 at current chess engine ELO rating levels. My port of Kaissa has a strength around 2250 ELO.

Jim.
gepasi
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Re: PDP-11 Chess VI (Belle) By Ken Thompson (1973) ported

Post by gepasi »

in my engine competition Chess VI has currently an ELO of 1807 (73 games). Kaissa has ELO 2112 (with 267 games).

I'm running this competition with 59 engines, playing blitz 2+0. I calibrated ELO by having Stockfish 17.1 (1CPU) pinned at 3780, which was its rating in CCRL when I started this.
Scientist, programmer, and general computer geek.